The prior art is replete with electronic sensors, transducers, and circuits that detect or measure physical phenomena. For example, an accelerometer can be realized as a miniature sensor component that detects movement, changes in physical orientation, vibration, shaking, or the like. Miniature accelerometers can be included in a variety of applications such as mobile devices, portable video games, and digital media players. An accelerometer in such a device can be used to detect whether the display of the device is oriented in a portrait mode or a landscape mode, to transition between sleep and active modes, to obtain user input (e.g., shaking the device might represent a user command), etc.
Accelerometers in portable devices are often implemented with capacitive sensing cells. In this context, a capacitive sensing cell includes a plurality of capacitors that are arranged and energized such that the capacitance of the cell varies with its acceleration. In typical applications, the measured difference in capacitance is converted into a voltage that can be processed or analyzed in an appropriate manner. In particular, a capacitance-to-voltage interface circuit can be used to convert the measured capacitance differential into a corresponding analog voltage. However, due to the relatively low voltage levels associated with such capacitance-to-voltage conversion, the analog voltage is usually amplified to provide adequate dynamic range for purposes of subsequent analog-to-digital conversion.
Conventional capacitance-to-voltage interface circuits utilize three primary elements or stages: a capacitive sensing cell; a first amplifier stage associated with the capacitance-to-voltage conversion; and a second amplifier stage associated with the analog voltage amplification. Notably, each amplifier stage includes at least one distinct operational amplifier device or circuit. Thus, at a minimum, the conventional architecture utilizes two distinct and separate operational amplifiers.